U.S. patent number 6,874,859 [Application Number 10/182,275] was granted by the patent office on 2005-04-05 for shaft/roller unit for tracked vehicles.
This patent grant is currently assigned to Split S.R.L.. Invention is credited to Enzo Duse.
United States Patent |
6,874,859 |
Duse |
April 5, 2005 |
Shaft/roller unit for tracked vehicles
Abstract
A shaft/roller unit for tracked vehicles which has a long life
and resistance to wear is formed by a shaft (54) which has a
shoulder (55) in its central portion, perpendicular to its axis,
and onto which two wholly hardened steel half-rollers (56, 57) are
fitted, one on each side of the shoulder, with the interposition of
antifriction bushings (58, 59), the half-rollers grasping the
shoulder (55) and, when they have been welded together along a
mating contact and locating surface (60), forming a unitary roller
which has a predetermined axial position on the shaft and can
withstand considerable axial stresses.
Inventors: |
Duse; Enzo (Bologna,
IT) |
Assignee: |
Split S.R.L.
(IT)
|
Family
ID: |
8175223 |
Appl.
No.: |
10/182,275 |
Filed: |
November 4, 2002 |
PCT
Filed: |
March 29, 2000 |
PCT No.: |
PCT/IT00/00109 |
371(c)(1),(2),(4) Date: |
November 04, 2002 |
PCT
Pub. No.: |
WO01/64503 |
PCT
Pub. Date: |
September 07, 2001 |
Foreign Application Priority Data
|
|
|
|
|
Mar 3, 2000 [EP] |
|
|
00830164 |
|
Current U.S.
Class: |
305/136;
305/137 |
Current CPC
Class: |
B62D
55/15 (20130101) |
Current International
Class: |
B62D
55/15 (20060101); B62D 55/14 (20060101); B60B
017/00 () |
Field of
Search: |
;305/136,100,137,124,139,195,194,13 ;301/13.2,40.2 ;152/396
;403/359.6 ;277/912 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
852044 |
|
Oct 1952 |
|
DE |
|
7638967 |
|
Apr 1977 |
|
DE |
|
7638967 |
|
Apr 1997 |
|
DE |
|
2003558 |
|
Nov 1993 |
|
RU |
|
002152488 |
|
Sep 1994 |
|
RU |
|
Primary Examiner: Jules; Frantz F.
Attorney, Agent or Firm: Sofer & Haroun, LLP
Claims
What is claimed is:
1. A shaft/roller unit for tracked vehicles including excavators
and tractors, said shaft/roller unit comprising: a roller formed by
a pair of axially drilled half-rollers hardened in their entirety,
bringing their hardness to more than 50 Rockwell C, and welded
together in the median plane of the roller, perpendicular to its
axis by means of flush welding with the addition of welded
material, each of said half-rollers being fitted on a shaft with
the sole interposition of a pair of antifriction bearings; the
shaft having a shoulder in its central portion, for abutment by the
antifriction bearings, and the shoulder having an outside diameter
larger than the diameter of the shaft, wherein the axial hole in
the half-rollers having a diameter smaller than the outside
diameter of the shoulder, wherein the half-rollers have a first
recess in the central portion of the roller for housing the
shoulder and wherein end flanges of each antifriction bearing are
directly in abutment with respective half-rollers on either side of
the shoulder so as to enforce a predetermined axial position of the
roller on the shaft, and providing for replaceability and exchange
of the entire shaft/roller unit.
2. A unit according to claim 1, in which the half-rollers are made
entirely of hardened steel.
3. A unit according to claim 1, in which the half-rollers have
respective mating mutual locating surfaces.
4. A unit according to claim 1, in which the axially opposed faces
of the roller have recesses for housing seals arranged flush with
the peripheral surface of the shaft.
5. A method of forming a replaceable shaft/roller unit for tracked
vehicles including excavators and tractors, comprising the
following steps: separate forging of two steel half-rollers to be
coupled with one another along a median plane of the roller,
perpendicular to its axis, hardening of the two separate
half-rollers in their entirety bringing their hardness to more than
50 Rockwell C, mechanical finishing of the two separate and
hardened half-rollers, pressing of bushings directly into each of
the two separate half-rollers, fitting of the two half-rollers each
carrying one of said bushings onto a shaft, one on each side of a
central shoulder of the shaft so that end flanges of each bushing
is in direct abutment with respective half-rollers on either side
of said shoulder, until mating coupling surfaces of the two
half-rollers are brought into contact, and welding the two
half-rollers along the mating surfaces, by means of flush welding
with the addition of weld material.
6. A method according to claim 5, in which, after the forging
stage, a further mechanical rough shaping stage is provided for
removing shavings from the two separate half-rollers, forming a
mating surface for the coupling of the two half-rollers.
7. A method according to or claim 6, in which the mating surface
for the coupling of the two half-rollers comprises a cylindrical
surface for the mutual location of the two half-rollers.
8. A unit according to claim 1, wherein each antifriction bearing
comprises: a first, flanged cylindrical bush which is pressed into
the axial hole in the respective half-roller and into the first
recess; and by a second cylindrical bush which is pressed into the
axial hole from the opposite side of the respective half-roller.
Description
FIELD OF THE INVENTION
The present invention relates to a shaft/roller unit for tracked
vehicles such as tractors, excavators and self-propelled machines
in general.
BACKGROUND OF THE INVENTION
In these machines, the tracks constitute a pair of steering tracks
with large surfaces for bearing on the ground, the arrangement of
which on the ground is changed by the operation of toothed drive
wheels which engage the tracks, whilst the weight of the vehicle,
which is often considerable, is supported by lower support rollers
which are free to rotate on upper sides or running surfaces of the
portions of the tracks which are bearing on the ground.
Further, upper rollers, on the other hand, have the function of
guiding the return portions of the tracks which are not bearing on
the ground.
When the tracked vehicle is in motion, the rollers rotate with the
tracks by friction, with a considerable component of sliding and
impact friction due to the discontinuity of the links and to the
different relative attitudes of the portions of track formed by the
links, which are not generally perfectly aligned.
This leads to considerable wear of the tracks and of the support
and guide rollers, further aggravated by the environment in which
these machines have to operate which causes loose and highly
abrasive earthy material to be carried along and interposed between
the tracks and the rollers.
The structure of the shaft/roller units for tracked vehicles is
therefore conditional upon the need to satisfy and to reconcile to
some extent different requirements imposed by the operating
conditions: the rollers should be particularly wear-resistant and
easily replaceable, the axial positioning of the rollers on the
shaft should be ensured by restraints which can withstand the
considerable axial thrusts which develop not only when the tracked
vehicle has to change its direction of travel or to rotate about
itself, but also when the machine discharges onto the tracks,
stresses oriented transversely relative thereto, in working
conditions; with regard to the considerable loads to be withstood,
the kinematic coupling between the movable roller and the fixed
shaft should provide adequately lubricated bearings (bushings)
protected by seals (also replaceable) which prevent leakage of
lubricant, on the one hand, and infiltration of abrasive earthy
substances into the coupling, on the other hand; in order to reduce
the contact area and the sliding speed of the seals, they should
have as small a diameter as the size of the shaft allows,
particularly in shaft/roller units used on tractors for which the
speed of movement, and hence the speed of the rollers, is quite
fast, with working cycles of considerable, almost continuous,
duration during movement.
Various arrangements have been proposed to satisfy and reconcile
these requirements and all are based on a structural concept which
provides for replaceability solely of the rollers or even solely of
their peripheral portions.
The cost of this is structural complications which greatly increase
the cost of the unit, make replacement operations onerous, and in
any case are at least partially detrimental with regard to other
requirements.
These problems are completely overcome by the shaft/roller unit for
tracked vehicles of the present invention which, since it is based
on the criterion of providing for replaceability and exchange of
the entire shaft/roller unit, achieves considerable structural
simplifications and substantial reductions in cost and ensures a
particularly long useful life of the unit, much longer than that of
most units of the prior art.
SUMMARY OF THE INVENTION
According to the present invention, which also relates to the
method of manufacture, these results are achieved by a shaft/roller
unit constituted by a shaft which has a shoulder in its central
portion, and on which two axially drilled half-rollers are fitted,
one on each side of the shoulder, the half-rollers having flanged
antifriction bearings which extend around the shaft and are in
abutment with the shoulder.
After they have been fitted on the shaft, the two half-rollers are
welded together to form a unitary roller which grasps the shoulder
and is coupled to the shaft in a captive manner, in a predetermined
axial position thereof.
This structure achieves the following results: the two half-rollers
can be hardened entirely and separately before assembly, which
ensures a longer life of the roller, the unit has good resistance
to axial stresses without structural complications or increases in
size at the ends of the shaft, and it is possible to use annular
seals which are arranged in close proximity to the shaft and have
small diameters and hence a small friction area and a low sliding
speed, so that they can also be used on relatively fast tracked
vehicles such as tractors.
BRIEF DESCRIPTION OF THE DRAWINGS
The characteristics and the advantages of the invention will become
clearer from the following description, given with reference to the
appended drawings, in which:
FIG. 1 is a combined front view and section showing a first
shaft/roller unit of the prior art,
FIG. 2 is a combined front view and section showing a second
shaft/roller unit of the prior art,
FIG. 3 is a combined front view and section showing a third
shaft/roller unit of the prior art,
FIG. 4 is a combined front view and section showing a shaft/roller
unit formed in accordance with the present invention.
DETAILED DESCRIPTION OF THE INVENTION
For a better understanding of the invention, it is appropriate to
examine closely the various technical arrangements which have been
adopted up to now.
FIG. 1 shows, in a combined front view and diametral section, a
shaft/roller unit for tracked vehicles of the prior art.
The unit comprises basically, a cylindrical shaft 1 having an
abutment shoulder 2, a pair of half-rollers or rims 3, 4, and a
pair of flanged hubs 5, 6.
The two rims, which are arranged reflectively symmetrically in
axial alignment with one another, are welded together to form a
unitary element, that is, a roller body, shaped generally as an
axially hollow reel with the sides recessed to house the flanges of
the respective hubs which are housed with their cylindrical
portions in the axial cavity of the hollow body.
The two hubs 5, 6 are fitted on the shaft 1, one on each side of
the shoulder 2, with the interposition of bushings 7, 8 in the form
of flanged cylindrical bushes.
The flanged portions of the two bushings are interposed between the
shoulder 2 and respective hubs 5, 6.
The two hubs are fixed to respective rims 3, 4 which form the
roller, by means of a plurality of bolts such as 9, 10, which
extend through the flanges of the hubs and are screwed into
threaded seats in the rims.
The inside diameter of the roller body is advantageously larger
than the outside diameter of the shoulder of the shaft 2 so that it
can be slid off the shaft after disconnection from at least one of
the hubs whereas, when the hubs are clamped onto the roller body,
the assembly of the roller body and the hubs forms a pincer which
grasps the shoulder so that the assembly is forced into a
predetermined axial position and can withstand considerable axial
stresses without translation on the shaft. It can also rotate,
together with the bushings 7, 8, on the shaft 1 which is normally
fixed and anchored to the side members or to fixed structures of
the tracked vehicle by means of end supports 11, 12, generally in
the form of saddles each provided with a respective profiled bell
or casing 13, 14 which is engaged on the shaft and has the combined
function, by adaptation of its profile to that of the sides of the
roller, of forming a chamber for housing seals and a labyrinth
which prevents, or at least limits, infiltration of extraneous
substances between the casing and the roller.
The seals are constituted by pairs of juxtaposed metal rings 15, 16
and 17, 18 with L-shaped cross-sections. Rings 19, 20, 21, 22 of
resilient material and of suitable, generally oval or circular
cross-section (O-rings), interposed, respectively, between the
rings 15, 18 and the casings 13, 14, and between the rings 16, 17
and the hubs 5, 6, keep the rings 15, 16 and 17, 18 in close
sealing contact, dividing the chambers housing the seals into two
hermetically separated compartments.
The resilient rings also ensure by friction that the rings 16, 17
of the two seals rotate together with the hubs 5, 6 and that the
rings 15, 18 remain stationary together with the casings 13, 14 and
the shaft 1.
To prevent rapid wear of the bushings 7, 8 and of the rings of the
seals, suitable lubrication is required and is ensured, for
example, by ducts 23, 24, 25 which are formed in the shaft 1, and
by means of which high-density oil can be conveyed into the
compartments disposed between the shaft 1 and the resilient
rings.
Two axial grooves 26, 27 formed in the upper portion of the shaft
enable the lubricant to be distributed throughout the length of the
bearings 7, 8 without altering the distribution of the load-bearing
hydraulic pressures which are developed in the lower portion of the
kinematic coupling between the shaft and the bushing when the
roller is in rotation.
Alternatively or additionally, the lubricant may be distributed by
means of channels formed in the hubs, as shown in FIG. 2 which will
be discussed below, and may be supplied through an opening 28 which
is closed by a plug and is formed in one of the rims constituting
the roller, and which communicates with an internal cavity of the
roller opening towards the hubs and towards the shoulder of the
shaft.
With further reference to FIG. 1, the structure of the shaft/roller
unit is completed by seals such as O-rings 29, 30, 31, 32 which are
housed in suitable annular grooves formed in the shaft 1 and in the
hubs 5, 6, and which form a seal against oil leakage in the
coupling between the hubs 5, 6 and the rims 3, 4 and in the
coupling between the casings 13, 14 and the shaft 1.
The shaft/roller unit described above has severe limitations of
durability due basically to wear of the running surfaces 33, 34 for
the tracks, which tends to reduce the thickness of the rims.
A hardening treatment, for example, by induction localized on the
running surfaces, confers greater hardness and hence abrasion
resistance. This measure increases useful life and is more
beneficial the greater is the depth of penetration of the
hardening. Once the hardened thickness of the running surface,
which is of the order of 10-20 millimeters, has been worn away,
wear proceeds rapidly in a dangerous and unpredictable and hence
uncontrollable manner which depends on operative conditions.
To prevent this problem, hardening of the rims in their entirety
would be desirable and can be achieved by special processes and
with suitable material (for example, a suitable steel).
Hardening of the rims in their entirety, whether it is performed
before or after the two rims are welded together, in any case
inevitably causes deformation of the roller which has to be
corrected by subsequent mechanical machining.
Machining which is necessary in any case is drilling to form the
threaded seats for the bolts 9, 10.
To prevent this problem and to simplify the structure to a certain
extent, it has been proposed, as described in U.S. Pat. No.
5,553,931 and illustrated in FIG. 2, to eliminate the bolts for
clamping the hubs, replacing them with split rings (Seeger or
Benzing rings).
In FIG. 2, the solid rims 35, 36, welded together, may be subjected
to a total hardening treatment which, in objects of such
considerable mass, does not reach the core but increases the depth
of hardening thereof so as to achieve a hardness of up to more than
45 Rockwell C even 20 mm from the surface.
The only mechanical machining to which the roller body formed by
the two rims 35, 36 has to be subjected is in fact the drilling of
the axial hole (with a diameter larger than the outside diameter of
the shoulder of the shaft) for housing two hubs 41, 42, and the
turning of two seats 37, 38 for two split rings 39, 40 for clamping
the two hubs 41, 42 which, in this case, have the shape and
function of sleeves of suitable thickness and length for centring
the roller body on the shaft and positioning it axially.
With this arrangement, the useful life of the roller is
considerably increased (greater hardness even within the material,
greater useful thickness of the running surfaces) but, otherwise,
the structure of the unit is similar to that of the unit of FIG. 1
and shares its structural complexity; the hubs 41, 42 have to be
machined accurately for coupling with the bushings on one side and
with the roller body on the other. Their length also has to be
calibrated to ensure that the roller body is positioned axially on
the shaft in accordance with the clearances calculated and that it
is clamped by the split rings. The machining has to be particularly
accurate because it is necessary to take account of the sum of
several tolerances relating to the length of the hubs, to the
thickness of the split rings, to the distance between the grooves
housing the split rings as well as, naturally, to the thickness of
the flanged bushings and of the shoulder of the shaft.
To reduce the complexity of this structure, it has also been
proposed to eliminate the shoulder of the shaft and to achieve the
axial positioning of the roller by other means.
As shown in FIG. 3, a roller constituted by two rims 43, 44 is
fitted directly on a cylindrical shaft 45 without any shoulder,
with the interposition of two flanged bushings 46, 47 pressed
directly into the axial hole in the roller with the flanges housed
and bearing in suitable recesses on the sides of the roller.
Axial positioning on the shaft is ensured by two lateral supports
48, 49 each of which forms a sleeve which is fitted on a respective
end of the shaft 45 and is urged into abutment with the flanged
portion of the respective bushing 46, 47.
The lateral supports 48, 49 are fixed to the shaft axially by means
of pins 50, 51 extending through suitable seats formed in the
supports and in the shaft 45.
The arrangement of FIG. 3, a variant of which is descried in U.S.
Pat. No. 5,251,913 (the lateral supports are cups closed at the
ends, forced onto the shaft and kept in position by the fixed
structures to which they are anchored) is further simplified in
comparison with that of FIG. 2, at least by the elimination of the
hubs, but has the very serious disadvantage that the seals,
generally indicated 52, 53, cannot be arranged flush with the
periphery of the shaft and are greatly spaced therefrom to allow
the sleeves of the lateral supports, which have to have an adequate
thickness, to come into abutment with the flanges of the
bushings.
For a given angular velocity of rotation, the larger diameter of
the seals leads to a greater speed of relative sliding between the
rings of the seals, a larger friction surface, a higher coefficient
of friction and, finally, heating incompatible with the use of the
unit in fast, self-propelled machines such as tractors or graders
operating, with reference to movements on the ground, with
practically continuous working cycles.
Moreover, the lateral supports and the ends of the shaft have a
somewhat larger size than in the previous arrangements which is not
acceptable in many applications.
The greater structural simplicity is thus detrimental with regard
to other requirements.
The common element of the arrangements described is that, in all
cases, the roller can be removed from the shaft in order to be
replaced, which inevitably involves laborious dismantling and
reassembly operations in the course of which it is quite difficult
for components of the unit other than the roller to be reused.
The fact that the unit can be dismantled into parts in order to
replace only the worn components thus constitutes a technical
disadvantage which has been overcome, permitting the production,
according to the present invention, of a greatly simplified
shaft/roller unit shown in FIG. 4.
The unit of FIG. 4 comprises, basically, a cylindrical shaft 54
having an abutment shoulder 44 in its central portion and a pair of
axially drilled half-rollers or rims 56, 57 fitted directly on the
shaft 54, one on each side of the abutment shoulder, with the
interposition solely of a pair of flanged bushings or antifriction
bearings 58, 59, the flanges of which are in abutment with the
shoulder 55.
The diameter of the axial hole in the half-rollers 56, 57 is
smaller than the outside diameter of the shoulder 55 of the shaft
so as to offer an adequate bearing and thrust surface for the
flanged portions of the bushings.
The two half-rollers are preferably coupled in the median plane of
the resulting roller, perpendicular to its axis, along a
cylindrical, male-female mating mutual locating surface 60.
They also have, in their coupling sides, respective recesses 61 for
housing the shoulder 55 of the shaft and the end flanges of the
bushings 58, 59 so that the flanged ends of the bushings 58, 59 can
be brought into abutment with the shoulder of the shaft when the
two half-rollers 56, 57 are side by side and located by the
coupling surface.
Welding along the periphery of the mating contact surface 60 of the
two half-rollers, thus positioned relative to one another, forms a
unitary roller which is coupled kinematically with the shaft and at
the same time is restrained in a predetermined axial position
thereon, with the ability to withstand considerable axial stresses
exchanged with the shaft.
The necessary seals, generally indicated 62, 63, are identical or
similar to those already described with reference to FIG. 1 or FIG.
2 and do not require further explanation. It will be noted merely
that they are arranged in close proximity to the surface of the
shaft 54, housed in chambers which are formed in recesses in the
sides of the roller constituted by the rims 56, 57 and are closed
by casings 64, 65 similar to those already described with reference
to FIG. 2.
The bushings and the seals are lubricated by shaft ducts and
possibly grooves, as in the case of FIG. 1.
According to the present invention, the following production method
may be implemented to produce the unit of FIG. 4.
First of all, the two half-rollers 56, 57 to be coupled together
are produced separately by forging (moulding) of steel.
Then, only if the desired dimensions are not achieved during the
forging, the two half-rollers are shaped roughly by a mechanical
turning process to bring them to a first level of finishing.
The two separate parts are then hardened in their entirety,
bringing their hardness to more than 50 Rockwell C.
The two separate and hardened half-rollers are machined further,
again separately, to correct the deformations caused by the
hardening.
In particular, the mating coupling surfaces 60, the axial hole for
housing the bearings, and the depths of the recesses 61 are
corrected to ensure the correct dimensions for housing the shoulder
55 of the shaft and the flanged portions of the bushings 58,
59.
These are the only finishing operations required to achieve the
desired tolerances of the two hardened parts.
At this point, the bushings 58 and 59 are pressed into the
respective seats with the flanged portions facing towards the
coupling faces of the two half-rollers. This operation is possible
because the two half-rollers are still separate.
In this connection, it should be pointed out that each of the
bushings 58, 59 may advantageously be constituted by two portions,
a flanged portion 58, 59, which is pressed in as already stated,
and a cylindrical portion 58A, 59A which is pressed in the opposite
side of the housing; this makes the insertion of the bushings even
easier.
With the bushings inserted, the two half-rollers are fitted on the
shaft 54, one on each side of the shoulder 55, until the flanged
portions of the bushings are brought into contact with the shoulder
55.
The mating locating surface 60 ensures the correct alignment of the
two half-rollers and ensures that the axial clearance of the
shoulder between the bearings is within the tolerances set.
The locating function could also be performed by the shaft itself
if the clearance of the bearings were kept within minimum values,
which condition is possible for rollers which are subject to little
loading transversely relative to the shaft.
Once the two half-rollers are coupled, they are welded along the
mating contact surface by known welding techniques, for example,
flush welding with the addition of weld material or even plasma
welding.
The unit is then completed, in conventional manner, by the
necessary seals and protective casings.
The replacement of worn rollers involves the replacement of the
entire shaft/roller unit, the overall cost of which, however, is
much less, owing to its structural simplicity, than the sum of the
costs resulting from operations to dismantle and reassemble the
units of the prior art, replacing only the worn parts.
Although the drawings relate to rollers with single rims,
naturally, the invention is not limited to rollers of this type but
also applies to rollers with double rims.
In order to satisfy contingent and specific requirements, an expert
in the art may apply to the above-described preferred embodiment of
the shaft/roller unit many modifications, adaptations and
replacements of elements with other functional equivalent elements
without, however, departing from the scope of the following
claims.
* * * * *